The field of art to which this invention pertains is radiation curable coatings.
The use of various polymers, such as polymethyl methacrylate, polycarbonate, polystyrene, styrene-acrylonitrile copolymers, polyesters and the like, have been used as replacements for glass in the manufacture of numerous articles. The polymers have the advantage over glass in that they are light in weight, have excellent shock resistance and are easily moldable. However, for some uses, such as optic uses, i.e., spectacle lenses, camera lenses, covers for lighting fixtures and headlights, the surfaces of the molded polymers are subject to abrasion and scratching. Attempts have been made to improve the abrasion and scratch resistance by coating the surface of the articles. Silicone resins and melamine resins have been used for this purpose. Such coatings are thermosetting types and require heating for long periods to produce cured coatings. The long heating periods reduce productivity and the high temperature can cause distortion of the molded polymer, which is thermoplastic. In an attempt to overcome these problems, U.S. Pat. Nos. 4,273,802 and 4,397,723 describe the use of radiation curable coatings to coat the surface of plastic articles to improve abrasion and scratch resistance. Such coatings are made from a blend of a compound, which contains at least 3 acryloyloxy groups, e.g., trimethylolpropane triacrylate and a compound, which contains only 2 acryloyloxy groups, e.g., the diacrylate ester of the diglycidyl ether of bisphenol A. Such coatings systems have improved abrasion and scratch resistance over the prior art; however, they are still somewhat lacking in these properties.